Rubicon lockers not engaging


Wranglerfix

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Good evening to all,

Over the past few months I have noticed an uptick on “some” of my Rubicon programmed pcms that will not engage the lockers as they should.

The pcms are properly programmed and the issue occurs randomly.

One client had no lockers for weeks and then they suddenly starting engaging.

The oem pcms engage the lockers as they should which led me to think there was a drive cycle or relearn that was needed.

I found the link below on the forum which I sent to a customer and it did not resolve the issue.


Customer, “That's not the problem i am having, new pcm wont recognize 4wd so lockers won't engage. Original pcm lockers and 4wd light work. I have tried all combinations and driven jeep for quite a few miles no luck with 4wd.drive and lockers.”

I am in need of some direction on this issue and all suggestions is greatly appreciated. @mrblaine @Jerry Bransford @Chris

Thank you in advance,

Mark
 
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Steel City 06

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If you haven’t already, take a good look at one of the later factory service manuals. There are wiring diagrams for the lockers and how they interface with the PCM, switches, and instrument cluster.


The wiring diagrams should give you a better idea of how the PCM is supposed to behave and what signals it should and shouldn’t send.

The factory locker system is much more complex than most aftermarket systems.

To physically engage a locker, all that has to be done is to send 12 volts to the appropriate locker pump. The sensors in the differentials are mere switches.

However, the wiring that tells the locker relays when the lockers are or are not to be engaged is significantly more complex. The system has to know it is in 4Low and within a certain range of speeds to engage, and it has to know what each engagement of the momentary switch is supposed to signal.

The FSM should also have a good description of the locking differential system in the section on the 216 front and rear differentials, and I seem to recall there may also be a section dedicated specifically to the locking differential system.

4Low in the Rubicon models also bypasses the clutch interlock, such that the engine can be started with the manual transmission in gear. This is by design to allow zero rollback starts on steep hills. I suspect this feature wouldn’t work if the lockers aren’t working either, especially if the issue is related to the transfer case position switch/sensor.
 
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Viking Jeeper

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If it is a PCM problem I would guess an override would fix it. In the thread below I did the "Independent Locker Control by Ken White". I can engage either locker at any time without PCM "permission".

 

mrblaine

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If it is a PCM problem I would guess an override would fix it. In the thread below I did the "Independent Locker Control by Ken White". I can engage either locker at any time without PCM "permission".

He is in the PCM fixing business. That isn't the answer.
 

mrblaine

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However, the wiring that tells the locker relays when the lockers are or are not to be engaged is significantly more complex. The system has to know it is in 4Low and within a certain range of speeds to engage, and it has to know what each engagement of the momentary switch is supposed to signal.
That part confuses me a bit. I've worked on a lot of them that did not have the correct program loaded into an aftermarket PCM. We fixed them by having the correct software loaded. We checked to see if the correct software was loaded by moving the t-case shifter to 4 low and watching for the 4wd light to trip on the dash. Once that light illuminates, the locker switch receives power and the ability to activate the locker pumps. Previous to the software download, the issue is the light on the dash would not come on in 4 low and without that, no power to the locker switch.

There were no delays or drive cycles or speed requirements needed to check the fix or functionality. This has been done several times and the only thing we have never checked is the max speed the light will be defeated. Since the light will function correctly at a stop, the rest is up to the owners to figure out.
 

JEEPCJTJ

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Maybe it's just me, and I sure can't help, but I, maybe we, need some clarification:

Customer, “That's not the problem i am having, new pcm wont recognize 4wd so lockers won't engage.
Does "won't recognize 4wd" include not even turning the 4wd light on?

Customer, “... Original pcm lockers and 4wd light work..."
I believe it worked before the new pcm, so I guess he's reinstalled the original pcm at least once. I do kinda wonder what he means by "Original pcm lockers" but it's probably poor sentence structure.

Customer, “... I have tried all combinations and driven jeep for quite a few miles no luck with 4wd.drive and lockers.”
All combinations that are available sounds like two different ways, either the new pcm or the old pcm. "All combinations" sounds like there are more possibilities than those two. That may also be a sentence type issue but if there are any other possibly tries he's made the details would help.

If it is a PCM problem I would guess an override would fix it.
Anyone can do that but I wouldn't do it for a customer that paid and expected something to work the way it was supposed to work from day one over a decade ago. Chrysler probably had a lawyer, or 20, suggesting it be the way it is. FWIW, I hate most lawyers.
 

Jerry Bransford

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As happy as I am that Mark was able to find and fix the software bug, it's disturbing that our lockers should be vulnerable at all to software problems.

Which is one reason I bypassed and replaced the entire Rube Goldberg factory locker control system with two simple on-off switches. 😊

RG-48.gif
 

mrblaine

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As happy as I am that Mark was able to find and fix the software bug, it's disturbing that our lockers should be vulnerable at all to software problems.

Which is one reason I bypassed and replaced the entire Rube Goldberg factory locker control system with two simple on-off switches. 😊

View attachment 219719
If you were designing a vehicle that the general public would drive on public roads that see ice and snow, you would set it up very similarly. The exact same symptom that disables the locker switch in 4wd, (4wd light on dash not illuminating) can be caused by many other things besides a software issue. And, those things are no more or less vulnerable to failure than owner installed switches and wiring to relocated pumps.